#include<bits/stdc++.h>
using namespace std;
#define OVERLOAD_REP(_1, _2, _3, name, ...) name
#define REP1(i, n) for (auto i = std::decay_t<decltype(n)>{}; (i) != (n); ++(i))
#define REP2(i, l, r) for (auto i = (l); (i) != (r); ++(i))
#define rep(...) OVERLOAD_REP(__VA_ARGS__, REP2, REP1)(__VA_ARGS__)
#define REP(i, l, r) rep(i, l, r+1)
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
using ll = long long;
using ld = long double;
using P = pair<ll,ll>;
struct Edge {
  int to; ll w;
};
using Graph = vector<vector<int> >;
//using Graph = vector<vector<Edge> >;
const ll INF = 2e18;
//const int INF = 2e9;
template<class T> using vc = vector<T>;
template<class T> using vv = vector<vector<T> >;
template<class T> using vvv = vector<vector<vector<T> > >;
template<class T> using pq = priority_queue<T>;
template<class T> using pq_g = priority_queue<T, vc<T>, greater<T> >;
template<class T> istream& operator>>(istream& i, vc<T>& v) { rep(j, 0, v.size()) i>>v[j]; return i; }
template<class T> ostream& operator<<(ostream& o, vc<T>& v) { rep(j, 0, v.size()) o<<v[j]<<" "; return o; }
template<class T> bool chmin(T& a, T b) {
  if(a > b) {
      a = b;
      return true;
  }
  return false;
}
template<class T> bool chmax(T& a, T b) {
  if(a < b) {
      a = b;
      return true;
  }
  return false;
}

int main() {
  // 高速化
  ios::sync_with_stdio(false);
  cin.tie(nullptr);

  // 小数点の出力桁数を指定
  cout << fixed << setprecision(10);
  // メイン
  int N, K;
  cin >> N >> K;
  vv<ld> dp(N+1, vc<ld>(N*6+1));
  dp[0][0] = 1;
  rep(i, 0, N-K) {
    rep(j, 0, N*6) {
      if(dp[i][j] == 0) continue;
      rep(k, 1, 7) {
        dp[i+1][j+k] += dp[i][j] / 6;
      }
    }
  }
  rep(i, N-K, N) {
    rep(j, 0, N*6+1) {
      if(dp[i][j] == 0) continue;
      rep(k, 4, 7) {
        dp[i+1][j+k] += dp[i][j] / 3;
      }
    }
  }

  vv<ld> dp2(N+1, vc<ld>(N*6+1));
  dp2[0][0] = 1;
  rep(i, 0, N) {
    rep(j, 0, N*6) {
      if(dp2[i][j] == 0) continue;
      rep(k, 1, 7) {
        dp2[i+1][j+k] += dp2[i][j] / 6;
      }
    }
  }

  ld ans = 0;
  REP(i, 1, N*6) REP(j, 1, N*6) {
    if(i > j) ans += dp[N][i] * dp2[N][j];
  }

  cout << ans << endl;

  return 0;
}